1. Field of the Invention
The present invention relates to a movement control mechanism for a contact-type vibrating probe for controlling the movement of a contact-type vibrating probe, the contact-type vibrating probe having a stylus with a contact portion at a tip end thereof to be abutted to a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus in an axial direction at frequency fl, and a detector for detecting change in vibration of the stylus by the vibrator.
2.Description of the Related Art
A height gauge (one-dimensional measuring machine), a coordinates measuring machine, and a profile measuring machine are known as measuring machines for measuring the configuration and/or dimensions of a workpiece. Various probes are used by the measuring machines in order to detect positional relation between the measuring machine and the workpiece. The probes are classified into non-contact-type probes and contact-type probes, and continuously measuring probes and trigger transmission probes.
A contact-type vibrating probe disclosed in Japanese Patent Laid-Open Publication No. Hei6-221806 is known as a contact-type trigger transmission probe (touch trigger probe) used for a coordinates measuring machine.
The contact-type vibrating probe disclosed in the publication includes a stylus having a contact portion to be in contact at a tip end thereof with a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus in an axial direction thereof by applying ultrasonic vibration, and a detector for detecting a change in the stylus"" vibration caused by the vibrator.
With the contact-type vibrating probe, since the vibration status of the stylus changes by touching the tip end, the end surface position of the workpiece can be detected by detecting the change in vibration status.
On the other hand, a contact-type vibrating probe is sometimes used for measuring the diameter of a small hole.
For measuring small holes, another contact-type probe shown in Japanese Patent Application No. Hei10-22047 has been proposed as a small size contact-type vibrating probe.
As shown in FIG. 24, the contact-type vibrating probe 100 includes a stylus holder 101, a stylus 102, a vibrator 103A and a detector 103B. A contact portion 102A to be in contact with the workpiece is provided at an end of the stylus 102 and a counterbalance 102B is provided at a base end of the stylus 102, so that the axially central position of the stylus 102 becomes the centroid position. When the stylus 102 vibrates in an axial direction, the centroid position becomes a node of vibration.
In the contact-type vibrating probe 100, the stylus 102 is composed of a thin stick member and the contact portion 102A is composed of a small sphere for adaptation to the small hole measurement. Further, since the thin stylus 102 is difficult to support at one point, the stylus holder 101 supports the stylus 102 at two points sandwiching the centroid position of the stylus 102.
The vibrator 103A and the detector 103B are made by dividing a piezoelectric element 103 stretching over the two supporting portions of the stylus holder 101. When the stylus 102 is resonated along the axial direction by the vibrator 103A, the nodes of vibration are generated at the centroid position of the stylus 102 and the supporting portions of the stylus 102 of the stylus holder 101.
According to the contact-type vibrating probe 100, since the stylus holder 101 supports the stylus 102 at the two portions sandwiching the nodes of vibration, the stylus 102 can be supported by the stylus holder 101 even when the stylus 102 is made by an extremely thin stick member, thus enabling the inner face measurement of a small hole having a large aspect ratio.
However, the following disadvantage occurs in continuous measurement along an inside wall of a small hole by the above-described contact-type vibrating probe 100.
Since the stylus 102 of the contact-type vibrating probe 100 has only a small axis diameter, the axis rigidity of the stylus 102 is lessened, so that the stylus 102 bends when the contact portion 102A is in contact with the workpiece, thus causing the so-called xe2x80x9cadhesion phenomenonxe2x80x9d.
The adhesion phenomenon causes little problem in detecting contact between the contact portion 102A and the workpiece. However, when continuous contact measurement is conducted along an end surface of the workpiece, a mechanical phase delay can be generated, thus resulting in mechanical deformation by the adhesive force causing a position error.
Further, the following problem also occurs. The above-described contact-type vibrating probe can detect contact with the workpiece with high accuracy since the detection signal sensitively changes by applying an extremely small contact force. On the other hand, it is impossible for the contact-type vibrating probe to discriminate which longitudinal position (a point on the contact portion surface defined as an angle on a plane orthogonal with the axis of the stylus) of the spherical contact portion touches the end surface of the workpiece. Accordingly, the contact-type vibrating probe has no sensitivity difference with regard to longitudinal direction of the spherical contact portion, so that it is impossible to know in which direction the contact portion touches the end surface of the workpiece. Accordingly, the contact-type vibrating probe is not suitably used as a probe for profiling measurement and continuous measurement.
An object of the present invention is to provide a movement control mechanism for a contact-type vibrating probe capable of preventing the adhesion phenomenon of the stylus caused by the contact with the workpiece and for conducting continuous measurement along the surface of the workpiece.
For attaining the above object, a movement control mechanism for controlling movement of a contact-type vibrating probe according to the present invention comprises a contact-type vibrating probe having a stylus provided with a contact portion at a tip end thereof to be in contact with a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus at frequency f1 in an axial direction, and a detector for detecting a change in vibration of the stylus by the vibrator. The movement control mechanism is characterized in having:
a support body mechanically connected to the stylus holder to move in three-dimensional space at a predetermined velocity in accordance with an external command;
a second vibrator for vibrating the stylus relative to the workpiece at a frequency f2 in a direction orthogonal to the axial direction of the stylus and also in a normal direction to a surface of the workpiece; and
a controller for controlling movement of the support body so that the state of a detection signal detected by the detector at contact of the contact portion with the surface of the workpiece remains constant when the contact portion touches the surface of the workpiece while vibrating the stylus by the second vibrator.
According to the above movement control mechanism of the contact-type vibrating probe, the contact-type vibrating probe can be used for continuous measurement of a surface of the workpiece while avoiding the adhesion phenomenon. As shown in FIG. 1(b), when the contact portion 102A of the stylus 102 is disposed adjacent to the surface of the workpiece W and is vibrated at a frequency f2 in a normal line direction to the surface of the workpiece by the second vibrator, the contact portion 102A touches and separates from the end surface of the workpiece W, thus conducting a tapping action.
At this time, since the vibration of the stylus 102 is either free in a non-contact state or is restricted by contact force F in a contact state, the vibration of the stylus 102 in the axial direction at the frequency f1 decreases amplitude A of the vibration in the axial direction of the stylus 102 in accordance with increase in the contact force F as shown in FIG. 2. A detection signal {overscore (V)} representing change (amplitude of the vibration, for instance) in the vibration detected by the detector takes turning value Va in accordance with vibration cycle (1/f2) of frequency f2 by the second vibrator, as shown in FIG. 3. When the stylus 102 moves in the B direction along the end surface of the workpiece W as shown in FIG. 4, the detection signal {overscore (V)} takes turning value of Va as shown in FIG. 3 and the turning value Va is constant for every vibration cycle.
On the other hand, when the moving direction of the stylus 102 is slanted relative to the end surface of the workpiece W as shown in FIG. 5, the detection signal {overscore (V)} is changed by the tapping action because the contact force of the contact portion 102A increases as the contact portion 102A gradually approaches toward the surface of the workpiece W and the turning value Va changes as shown in FIG. 6. Accordingly, by controlling the movement of the contact-type vibrating probe 100 by the controller so that the change in state represented by the turning value Va is constant (in other words, so that the detection signal {overscore (V)} takes predetermined turning value Va and the turning value Va is constant), the contact-type vibrating probe 100 can move along the surface of the workpiece W to conduct continuous measurement of the surface of the workpiece W. Further, by setting the turning value Va so as not to exceed a predetermined value, the mechanical phase delay can be set extremely low, thus preventing error in the detection position in accordance with the adhesion phenomenon to conduct the continuous measurement of the end surface of the workpiece.
Specifically, as shown in FIG. 7, the movement control is conducted so that the stylus 102 moves toward and away in a direction C along the vibration by the second vibrator orthogonal with the axial direction of the stylus. By repeating the movement in the direction B and the direction C, the stylus 102 can move along the surface of the workpiece W.
In the present invention, the controller may preferably move the support body in a direction orthogonal with the line of normal to the end surface of the workpiece.
Specifically, the controller may preferably control the driving mechanism for moving the support body along the X-axis and the Y-axis directions of an XY positioning table for the workpiece and along the Z-axis direction normal to the XY table surface.
By employing the above controller, when the inside wall of a small hole W1 formed on the workpiece W is measured as shown in FIG. 8, the contact portion 102A can move along the inner circumference direction H of the small hole, thus conducting continuous measurement of the opening of the small hole W1. Further, as shown in FIG. 8, since the contact portion 102A can move in depth direction D of the small hole W1, continuous measurement of the small hole W1 in depth direction is possible.
Another object of the present invention is to provide a movement control mechanism of a contact-type vibrating probe which can employ the above contact-type vibrating probe as a probe for profiling measurement and continuous measurement and the configuration of the workpiece can be measured with high accuracy.
For attaining an object of the present invention, a movement control mechanism for controlling movement of a contact-type vibrating probe comprises a contact-type vibrating probe having a stylus provided with a contact portion to be in contact at a tip end thereof with a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus at frequency f1 in an axial direction, and a detector for detecting a change in vibration of the stylus by the vibrator. The movement control mechanism is characterized in having:
a support body mechanically connected to the stylus holder to move in three-dimensional space at a predetermined velocity and direction in accordance with an external command;
a second vibrator for vibrating the stylus relative to the workpiece at a frequency f2 along a surface of the workpiece; and
a controller for controlling movement of the support body or the workpiece so that the state of a detection signal detected by the detector at contact of the contact portion with the surface of the workpiece remains constant when the contact portion touches the surface of the workpiece while vibrating the stylus by the second vibrator.
According to the operating control mechanism of a contact-type vibrating probe, the contact-type vibrating probe can be used for profile measurement and continuous measurement while detecting the longitudinal position of the contact portion in contact with the workpiece as follows:
As shown in FIG. 1(b), the contact portion 102A of the stylus 102 is brought into contact with the end surface of the workpiece W and the amplitude A of axial vibration of the stylus 102 is detected as a detection signal detected by the detector. The amplitude A is the largest when the contact portion 102A is not in contact with the surface of the workpiece W. When the contact portion 102A is pressed onto the surface of the workpiece W to increase the contact force F, the amplitude A decreases. The value of the amplitude A of the contact force which can maintain the contact with the workpiece W and the contact portion 102A and does not cause damage on the stylus 102 is set as the predetermined value (threshold value) A0 as seen in FIG. 2.
The stylus 102 is vibrated by the second vibrator at the frequency f2 while the contact portion 102A is in contact with the surface of the workpiece W at a predetermined contact force so that the detection signal takes the threshold value AO.
When the vibrating direction caused by the second vibrator at frequency f2 is along the surface of the workpiece W as shown in FIG. 9, the amplitude A as the detection signal detected by the detector takes constant value A0 smaller than the amplitude G2 representing the amplitude during free vibration of the stylus 102 as shown in FIG. 10. There is no change in the condition shown in FIG. 10 after moving the stylus 102 along a vibrating direction M1 by the second vibrator.
On the other hand, when the vibrating direction M1 of the vibration by the second vibrator at frequency f2 is slightly slanted relative to the surface of the workpiece W as shown in FIG. 11, the contact force of the contact portion 102A relative to the surface of the workpiece W changes by the vibration of the second vibrator, and the amplitude A detected by the detector also changes in accordance therewith. This is because the contact force changes because the contact longitudinal position on the contact portion 102A before vibration by the second vibrator is different from the contact longitudinal position during vibration, which causes change in the contact force.
Accordingly, when the stylus 102 is moved along the vibrating direction M1 of the second vibrator, the amplitude A detected by the detector decreases in a direction toward the surface of the workpiece W and increases in a direction away from the surface of the workpiece as shown in graph G3 of FIG. 12.
In the present invention, when the amplitude A detected by the detector changes while the stylus and the workpiece are relatively vibrated along the surface of the workpiece by the second vibrator, the controller controls the movement of the contact-type vibrating probe and/or the workpiece so that the amplitude A as the detection signal is constant, so that the contact-type vibrating probe can move in a direction M2 along the end surface of the workpiece W to conduct continuous measurement of the surface of the workpiece W at a constant contact force.
In the present invention, since the above second vibrator is for vibrating the stylus at the frequency f2 along the surface of the workpiece and the workpiece has a three-dimensional configuration, the second vibrator preferably vibrates in three-dimensional directions. Specifically, with reference to a space coordinate system represented by an X-axis, a Y-axis, and a Z-axis, the second vibrator may preferably include an X-axis vibrating mechanism for vibrating the stylus in the X-axis direction, a Y-axis vibrating mechanism for vibrating the stylus in the Y-axis direction, and a Z-axis vibrating mechanism for vibrating the stylus in the Z-axis direction.
By arranging the second vibrator in the above-described manner, the vibrating direction of the second vibrator can be controlled three-dimensionally, thus conducting profiling measurement and continuous measurement of a workpiece having complicated three-dimensional configuration. When the inside wall is measured along the circumferential direction of a cylindrical workpiece, only the X-axis vibrating mechanism and the Y-axis vibrating mechanism are required for the second vibrator and the Z-axis vibrating mechanism is not necessary. In short, the arrangement of the second vibrator can be determined in accordance with intricacy of the configuration of the workpiece.
In the movement control mechanism of a contact-type vibrating probe, the controller may preferably control the movement of the support body or the workpiece so that the change in state quantity of the detection signal in accordance with the contact of the contact portion with the surface of the workpiece is minimized when the contact portion is in contact with the end surface of the workpiece while vibrating the stylus by the second vibrator.
Specifically, the controller may be arranged to drive a driving mechanism for relatively moving the support body in the X- and Y-axis directions of the XY table for the workpiece put on and the Z-axis direction normal to the XY table surface, to obtain the state quantity of the detection signal from the detector and to control the movement of the respective driving mechanism to minimize the state quantity, thus moving the support body and/or the workpiece relative to the surface of the workpiece.
According to the above controller, since the movement of the support body and/or the workpiece is controlled while obtaining the detection signal detected by the detector, the contact portion 102A can move along the end surface of the workpiece W, thus conducting profiling measurement of the workpiece with a minimum contact force.
Further, the movement control mechanism of a contact-type vibrating probe may preferably further include a vibrating direction controller for controlling vibrating direction of the second vibrator so that, when the contact portion touches the surface of the workpiece and the stylus and the workpiece are relatively vibrated by the second vibrator, the change in state of the detection signal including a predetermined value is minimized for the detection signal from the detector to take a predetermined value.
With the above-described vibrating direction controller, the vibrating direction of the vibration by the second vibrating direction can be changed to a direction relative to the surface of the workpiece in accordance with the change in the detection signal. Accordingly, since the vibrating direction of the contact portion to be in contact with the workpiece by the frequency f2 can be always maintained toward the surface of the workpiece, the profiling measurement and continuous measurement of the workpiece are possible without knowing the approximate configuration of the workpiece in advance.
In the present invention, following specific arrangement may preferably be used. The movement control mechanism may preferably further include an escape circuit for suspending the movement control by the controller when the change in the state of the detection signal cannot be maintained at a constant level and for moving the support body so that the contact portion is not in contact with the surface of the workpiece.
When a configuration of a bottom of a hole or a workpiece having a wall in advance of the stylus is to be measured, the workpiece and/or the contact-type vibrating probe can be damaged when the stylus continues to be moved by the controller even when the contact portion reaches the wall.
On the other hand, when the movement control mechanism of the contact-type vibrating probe has the above-described escape circuit, the movement control by the control circuit can be stopped and the support body can be moved so that the contact portion is not in contact with the surface of the workpiece, and the workpiece and/or the contact-type vibrating probe can be prevented from being damaged. Specifically, the support body and/or the workpiece may be moved, for instance, in a direction opposite to the relative moving direction of the stylus by the controller.
In the present invention, the vibrator and the second vibrator may include more than one vibration element disposed around the axis of the stylus at a predetermined angle, for instance, 90 degrees. Alternatively, the first vibrator and the second vibrator may include more than two vibration elements disposed around the axis of the stylus at an equal interval.
The above-described vibration element may be piezoelectric element. The first vibrator and the second vibrator can be constituted by disposing the piezoelectric elements on a surface of a cylindrical body for a stick-shaped stylus to be inserted, where two piezoelectric elements are arranged on the cylinder surface at 90 degrees relative to each other, or three piezoelectric elements may be arranged on the cylinder surface spaced at 120 degrees at an equal interval.
By synchronously an electric signal applying of frequency f1 to the respective piezoelectric elements, since the force of the piezoelectric elements in the axial direction is not cancelled, the stylus can be resonated in the axial direction.
On the other hand, when the frequency f2 is applied to the plurality of piezoelectric elements provided around the axis in 90 degrees or at equal intervals, since the force of the stylus in the flexural direction is combined and applied to the stylus, the piezoelectric elements are capable of setting the vibration surface of the vibration by the second vibrator in any desired direction around the stylus.
In the present invention, the above-described second vibrator may be provided as a body independent of the vibrator, thus vibrating the stylus holder in two directions mutually orthogonal with each other relative to the axis line of the stylus.
Specifically, the second vibrator may have a serial disposition of a vibration element for vibrating the stylus holder in one direction and another vibration element for vibrating the stylus holder in the other direction.
Alternatively, the second vibrator may have a parallel disposition of a vibrator for vibrating the stylus holder in one direction and another vibrator for vibrating the stylus holder in the other direction.
Since such second vibrator is provided as a body independent of the first vibrator, the present invention can be implemented using the contact-type vibrating probe having a conventional vibrator, and only the stylus can be easily exchanged while leaving the second vibrator as it is.